Programmed cell death is recognized as an integral part of the biological repertoire of multicellular organisms where an intrinsic suicide mechanism can be activated either as a response to an invading pathogen or to specific signals generated during the normal course of the development of the animal. Apoptosis, from the Greek word for the falling off of leaves, is a morphologically distinct form of this death process hallmarks of which include plasma membrane bleb formation, retraction of cellular processes (e.g., neurite retraction during neuronal apoptosis), decrease in cellular volume, cellular rounding, nuclear fragmentation, and cellular budding to produce apoptotic bodies (Kerr J. F. R. and Harmon, B. V., 1991; Cold Spring Harbor Laboratory Press: New York, p. 321). The body utilizes apoptosis in many ways, including, for example, tissue remodeling during growth and development, deletion of autoreactive lymphocytes from the immune system, and elimination of cells containing damaged DNA.
Apoptosis-inducing stimuli are diverse, and include normal physiological signals, such as hormones that trigger deletion of cells during differentiation or involution of tissues or organs, maturation of organ systems as, for example, in the immune system, and removal of cells that have sustained some form of damage. Alternatively, cells may be already primed to undergo apoptosis, with removal of either intracellular apoptosis-inhibitory factors or withdrawal of important extracellular components, such as growth factors, providing the signal. Other apoptosis signals are also important from the biomedical perspective. These include radiation, hyperthermia, calcium influx, glucocorticoids and cytotoxic agents.
In adult tissues, apoptosis is involved in tissue homeostasis, physiological responses to hormones, and pathological response to pharmacological and toxic substances. Apoptotic deletion of cells is observed in both rapidly and slowly dividing tissues, for example in the intestinal crypts and the liver. Hormonal regulation of xe2x80x9ccell growthxe2x80x9d is often mediated by blocking apoptosis. For example, physiological lowering of trophic hormone levels results in apoptosis in the premenstrual endometrium and in the breast epithelium at the end of the menstrual cycle. In the prostate, testosterone inhibits apoptosis; removal of androgen stimulation by castration in rats results in regression and atrophy of the prostate due to cell death. Apoptosis also plays a major role in immunological control. During maturation of thymocytes, cells recognizing self-antigens are clonally deleted by apoptosis to allow immunological tolerance. In the liver, numerous drugs, hormones, and environmental toxins induce liver enlargement and promote preferentially the growth of preneoplastic foci. Regression of these foci following removal of the stimuli is often accompanied by extensive apoptosis, suggesting that these agents affect growth by blocking apoptosis. Radiation, mild hyperthermia, cancer chemotherapeutic agents, and chemical carcinogens induce apoptosis in certain cells and tissues. Apoptosis is observed to occur spontaneously in a wide variety of neoplasms.
Many infectious agents that modulate the immune system for their survival may do so by affecting the normal apoptosis process. It has been demonstrated that many viruses express anti-apoptotic factors as part of their initial, productive infection of mammalian cells (White and Gooding, xe2x80x9cRegulation of apoptosis by human adenovirusesxe2x80x9d p. 111-142 in APOPTOSIS II: THE MOLECULAR BASIS OF APOPTOSIS IN DISEASE, Tomei and Cope (Eds). Cold Spring Harbor Laboratory Press, New York (1994)). Infectious agents other than viruses also have been demonstrated to modulate apoptosis in vivo. (Zychlinski et al., Nature 358:167-169 (1992)).
Evidence for apoptosis in neurodegenerative disease has been obtained in chronic cases, such as Alzheimer""s disease, multiple sclerosis, ataxia telangiectasia, and prion-induced neuronal cell death and also, in acute diseases such as stroke (Linnick et al., Stroke 24:2002-2009 (1993); Mattson et al., J. Neurosci. 12:376-389 (1992); Scher, R. S., Bio/Technol. 12:140-144 (1994); Olson, L., Exp. Neur. 124:5-15 (1993); Forloni et al., Nature 362:543-546 (1993)).
Other disease processes where disregulated apoptosis has been implicated include, for example, various malignant and pre-malignant conditions such as B cell lymphoma and chronic lymphocytic leukemia, heart disease such as ischemic cardiac damage and chemotherapy-induced myocardial suppression, immune system disorders such as AIDS and type I diabetes, intestinal disorders such as inflammatory bowel disease and radiation- and HIV-induced diarrhea, and kidney disease such as polycystic kidney disease and anemia/erythropoiesis.
Accordingly, disregulation of programmed cell death is variously implicated in human disease. Thus, there is a great clinical need to elucidate the underlying molecular basis of the apoptosis mechanism and its role in disease which, in turn, will enable the development of compositions and methods for modulating the proteolytic, endonucleolytic, and morphogenetic aspects of apoptosis. The present invention satisfies this need and provides related advantages as well.
The present invention provides methods and compositions for modulating the apoptotic activity of interleukin-1xcex2 converting enzyme (ICE).
The present invention further provides methods and compositions for alleviating pathological conditions associated with apoptotic mechanisms.